6.6-stable review patch. If anyone has any objections, please let me know.
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From: Gui-Dong Han hanguidong02@gmail.com
commit 14c9ede9ca4cd078ad76a6ab9617b81074eb58bf upstream.
In the fts_read() function, when handling hwmon_pwm_auto_channels_temp, the code accesses the shared variable data->fan_source[channel] twice without holding any locks. It is first checked against FTS_FAN_SOURCE_INVALID, and if the check passes, it is read again when used as an argument to the BIT() macro.
This creates a Time-of-Check to Time-of-Use (TOCTOU) race condition. Another thread executing fts_update_device() can modify the value of data->fan_source[channel] between the check and its use. If the value is changed to FTS_FAN_SOURCE_INVALID (0xff) during this window, the BIT() macro will be called with a large shift value (BIT(255)). A bit shift by a value greater than or equal to the type width is undefined behavior and can lead to a crash or incorrect values being returned to userspace.
Fix this by reading data->fan_source[channel] into a local variable once, eliminating the race condition. Additionally, add a bounds check to ensure the value is less than BITS_PER_LONG before passing it to the BIT() macro, making the code more robust against undefined behavior.
This possible bug was found by an experimental static analysis tool developed by our team.
Fixes: 1c5759d8ce05 ("hwmon: (ftsteutates) Replace fanX_source with pwmX_auto_channels_temp") Cc: stable@vger.kernel.org Signed-off-by: Gui-Dong Han hanguidong02@gmail.com Link: https://lore.kernel.org/r/20250606071640.501262-1-hanguidong02@gmail.com Signed-off-by: Guenter Roeck linux@roeck-us.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/hwmon/ftsteutates.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
--- a/drivers/hwmon/ftsteutates.c +++ b/drivers/hwmon/ftsteutates.c @@ -423,13 +423,16 @@ static int fts_read(struct device *dev, break; case hwmon_pwm: switch (attr) { - case hwmon_pwm_auto_channels_temp: - if (data->fan_source[channel] == FTS_FAN_SOURCE_INVALID) + case hwmon_pwm_auto_channels_temp: { + u8 fan_source = data->fan_source[channel]; + + if (fan_source == FTS_FAN_SOURCE_INVALID || fan_source >= BITS_PER_LONG) *val = 0; else - *val = BIT(data->fan_source[channel]); + *val = BIT(fan_source);
return 0; + } default: break; }